37 th S.C. meeting - LNF December 1 th , 2008

1. 37th S.C. meeting - LNF December 1th, 2008 ? presented by V. Lucherini LNF- INFN

2. Hydrogen “Isotopes” Nucleus charge: +1 Reduced mass: ≈me Protiumpe-(usually referred to as “Hydrogen”) Deuteriumde- Tritiumte- Muiume- (known as Muonium) (... but improperly: Muonium is  ) Piiume- (not yet discovered) (Pionium, , has however been discovered) KaiumKe- (not yet discovered) Sigmiume- (not yet discovered) ........... ......... ............

3. Study of new Hydrogen-like Atoms: Why? Add to the list the antihydrogen Precision tests of QED Precision measurements of particle properties Tests on fundamental symmetries

4. CPT INVARIANCE CPT INVARIANCE fantastic precision, but .... Direct measurements Indirect measurement

5. Which mass is really measured: mK-AND mK+? ? PDG 2008 All measurements regard K-, with just one exception mixing the two charge states (..and even so there exists a puzzling situation). Precision measurement of K+ mass never done !

6. The (K+e-) atomic system is, many respects, a light hydrogen “isotope” (except for the spin-spin interaction), whose correct name is Kaium. Kaium has, until now, never been seen. It is formed when slow K+ are further slowed down until their velocity is decreased to a value of the order to the velocity of the electrons orbiting in the external levels of the atoms of the material in which it is slowed down (that is of the order of , in units of c). DANE is a unique source of slow and clean charged kaons, whose negative component, the K-, has (and is) already been successfully used to form and study kaonic atoms, in which a slowed down K- bounds itself to one of the atomic nuclei of the struck material. DANE is the only place, today, in which the slowest K+ are produced. And hence It can be the optimal place where the formation of Kaium could be detected, slowing down the slow K+ from the  decays almost at rest. DANE will reach, at the end of the SIDDHARTA data taking, its best perfomance in the present configuration, i.e. with no solenoidal magnetic field along the I. R.

7. K+ and e- are bound The reduced mass  of the system is very close to the e- mass ( ≈ 0.511 MeV) The (K+e-) binding energy is, as for ordinary H, of the order of few eV. Atomic radius ≈ 1/2 Å Radiative transitions generate photons in the UV, Visible, IR region of the e.m. Spectrum Levels determined by QED, not affected by strong interaction K- and p are bound The reduced mass  of the system is much bigger than the e- mass ( ≈ 324 MeV) The (K-p) binding energy is much bigger than ordinary H, of the order o few keV. Atomic radius ≈ 1/150 Å Radiative transitions generate photons in the X-ray region of the e.m. Spectrum Levels determined by QED, influenced by the strong interaction

8. The slowing down of the ≈120 MeV/c K± (K.E. ≈ 13 MeV) generated by the decay of the  mesons produced by DANE in a given material proceeds following the well know Bethe & Block relation. When, however, their velocity reaches a value of the order of  (with respect to c), the K+ can capture an e- from one of the atoms of the material, and becomes a neutral system. Its further slowing down follows then the relation for fast moving neutral atoms. There can occur, however, another process: the ionization (i.e. the loss of the e-) in a collision with an atom or molecule of the material. This process has high probability, since the binding energy is of the order of eV, while the kinetic energy of the neutral system is still of several KeV. When the K+ has slowed down to a velocity ≈ it will then undergoes a cycle of Charge- Exchange (ChEx) reactions (capture and loss of an e-), until its kinetic energy is so decreased that it will be no more able to capture or lose an e-. Accordingly, It will emerge from such ChEx phase as a bare K+ or as a (K+e-), respectively. The ChEx phase is typically very fast, lasting ≈ 1 ns.

9. KAIUM cannot be discovered with the same technique as “Muonium” The K+ spin is 0, while that of + is 1/2 KAIUM can be discovered in searching for the emission of visible light generated by the decay of KAIUM from excited to lower levels, in particular by looking for the Balmer transitions (as the Ha )

10. Toward detection of KAIUM formation Grasping the method The processes undergoing during the slowing down of a heavy(>> me) positive particle in matter are, within few %, identical, irrespective of its mass. The results obtained for a positive (heavy) particle of a given mass can be directly applied to a (heavy) particle of different mass, just scaling its kinetic energy according to their mass ratio:  the crucial point is to compare results at the same particle velocity. Many results, both experimental and theoretical, exist regarding Hydrogen formation by impact of slow p on targets made of different gases. In particular, a whole set of results have been obtained on Hydrogen formation by impact of slow p on different gases, by looking for the Balmer photons emitted in the de-excitation of the formed Hydrogen atoms. The results obtained by Hydrogen formation due to impact of slow p on gases can be smoothly exteded to the case of impact on the same gases of equivalently slow K+.

11. From Literature (years ‘60-’80) Motivation: study of upper atmosphere phenomena (aurora) and diagnostics for studies on fusion. Method: TOF technique to measure the electronic capture cross section with formation of H in (n,l) states by collision of slow protons on gases: H+ + A --> H(n,l) + A+. Data on different gases: H2, He, Ar, Ne, N2, O2, Xe, Kr. Very low pressure: P~m Torr (~10-2-10-4 mbar). Measurement of cross section of formation by Charge Exchange and of destruction by ionization collision. Energy range: 1-400 keV. Half lives < 200ns. Gass Cell Lengths ~50-80 cm. Typical measurement collision of a slow p beam on a gas and observation of radiation emitted by Neutralized H atoms.

12. Example: Ha (n=3  n=2) emission of 20 keV p on N2 Three contributions for BalmerHa from capture in states 3s, 3p e 3d with half lives of (respectively): 158 ns, 5.4 ns and 15.6 ns.

13. Cross sections (x10-18) for the capture of slow p in He leading to Hydrogen formation in some (n, l) states 3d The cross sections are “huge” (~ Mb), but ionization is huge too

14. Cross section for Balmer Ha emission from slow p in He due to Hydrogen de-excitation from n=3 to n= 2 levels EMISSION CROSS SECTION (cm2) Proton Kinetic Energy (keV)

15. A first crude estimation of Ha photons from Kaium formation at DAFNE (He gas, pressure 10 mbar, cell length 10 cm) Daily integrated Luminosity with upgraded DAFNE at ~ mid ’09: 20 pb-1×day-1 (hopefully a conservative prevision...) Daily producedcharged kaons: 3.1×107day-1 Daily effectivecharged kaons (assuming 20% acceptance): 6.2×106day-1 Daily effectivecharged kaons (assuming 0.5% the efficiency to slow down the effective charged kaons to the useful range of velocities in a low pressure gas cell): 3.0×104day-1 ProducedHaphotons (l~ 656 nm) from Kaium formation and Balmer radiative decay: 1.5×102day-1 Detected Balmer Haphotons from Kaium formation and radiative decay, assuming a 40% detection efficiency: 6.0×101day-1 ~2000 Haphotonsin ~1 month of run. Enough for a Yes/No search to assess the discovery of KAIUM and the ability of DAFNE to produce it (... if the background is not overwhelming)

16. Assessing the background in KAIUM search at DAFNE In an ideal cell containing pure He, enclosed by light tight walls, any crossing ionizing particle can produce visible light by exciting the He atoms, that, subsequently, can decay radiatively with Balmer transitions. A trigger selecting only charged kaons will reject all light contamination due to any other particle, except kaons or their interaction/decay products. Anyway, the background photons will not have the wave lenght of Hydrogen, but of He lines. Å Balmer H lines can be generated only if contaminants containing H are present in the cell that are excited by the triggered particles. H contaminants are at room temperature and hence have negligible Doppler broadening. On the opposite, Ha photons from Kaium are expected to experience large Doppler effect. Finally, K- can produce only background photons, since only K+ can produce Kaium.

17. Photons emitted in Kaium de-excitation have huge Doppler shift me- = 0.511 mK+ 494 MeV K.E. ≈ 20 KeV 1) K.E. ≈ 24 eV He K.E. ≈ 70 meV hn Kaium Capture: mK+ 494 MeV K.E. ≈ 20 KeV – 24 eV He+

18. How to fight the background of light in KAIUM search at DAFNE Triggering on Charged Kaons Selecting Doppler shifted Ha lines Disentangling from K+ or K- collected light Ability to detect single photons

19. A GENDAKEN EXPERIMENTAL SET UP WHITE Box containing the Optical Spectroscopy system and the photon detectors Not to scale, but ~ 50 cm He cell Thin scintillators of the charged Kaon Detector Charged Kaons Brake material by means of back-to-back correlated coincidence and Tof selection of slow K+/K- K+ Beam pipe K- Thick scintillator for the K+/K- selection by means of the different timing of stopped K+/K- fate: prompt interaction for K- , smooth decay for K+ ... and the DAFNE RF signal to provide the clock

20. Disentagling K+ from K- by time information Particles from K- interaction Particles from K+ decay π- π- p effect of Gate width μ+ Time = (Tofone – tofino) – (time of flight path) (by kind permission from FINUDA)

21. To appear in EXA2008 (Vienna, 15-18 September, 2008) Proceedings

22. UPDATE: MonteCarlo simulation (Andrea Fontana, INFN Pavia)

23. The multiplicative effect of the Charge Exchange cycles Once entered in the window of capture velocities, the K+ can strip an He atom of one e-, forming a Kaium atom. If the Kaium atom is formed in an excited level it can, subsequently, decay radiatively, emitting, for instance, the Ha photon. The Kaium atom can also undergoes a collision, resulting ionized before de-exciting. The ionization process, however, destroyes the Kaium atom, but does not destroy the K+: it survives and can again capture an e-. The ionization increases the probability to get the searched photon (Ha for instance), since it gives a further chance for a capture process in the good level. The more the charge exchange cycles, the more the probability to get the wanted photon. Of course, the finite life time poses a limitation, but the overall charge exchange cycle is much faster (equal or less 1 ns) of the K+ lifetime. The higher the gas target pressure, the better is

24. Two alternative lines of action • “Low Yield” • - Fast photon detector able to • operate in single photon mode • (as PMs, APDs), coupled to • - Interference filters. • - Adapting optical system. • - Charged Kaon Detector. • - Detector for K+ vs. K- selection. • Advantages • Triggerable system • Disadvantages • - Only a narrow wavelenght region of spectrum explored on each exposure. • “High Yield” • - Standard, CCD based, spectroscopy set-up, • comercially available • - Adapting optical system. • Advantages • Large region of spectrum explored simultaneusly • Disadvantages • - Not triggerable. The level of the background also imnportant to define the optimal choice

25. Possible test for production and detection of Balmer-a light by stopping slow protons in He to allow the tuning of the experimental parameters and check the Monte Carlo simulation • Light collection optimization • - Project of the light collection and • detection chamber • - Study of geometrical layout • - Study of wall reflectivity • Detectors • - Avalanche Photo Diode (APD), • - Photo Tupes (PM) • - Interference filters • - CCD spectroscopy set-up • Measurement proposal • - Signal search • - Background studies • Process of electronic capture and • Hydrogen formation by collision of • p in He gas. Ioninization Collisions. • Production of Balmer-a light • - Yield estimate • ....................... The LABEC Laboratory of Florence has nicely suited slow proton beams

26. LABEC Laboratory of Florence extracted proton beams of up to 6 MeV energy Intensity: from “single proton” to few tens of mA fast pulsed beam line

27. Set-up for test at LABEC (mid of February 2009) Reflective inner coating p Light output He cell Detector 1 Hamamatsu APD (SiPM), 3 mm2 Interference filter Detector 2 Focusing lenses Monochromator CCD

28. Avalanche Photo Diode Tipical amplitude spectrum with extremely low intensity source.

29. Interference Filters Manifactured by CVI laser optics: different coatings on a glass (BK7) substrate. Thickness: ~6mm (0.25¨)

30. Next steps - An interdisplinary effort is under way to fully undersand the process of Kaium Formation and Detection - Several reasearchers have already expressed their interest in the topic, incuding people working at LNF (and elsewhere) in the field of atomic spectroscopy - A first test is foreseen at the LABEC accelerator in Florence in mid February 2009 to measure Hydrogen formation by slow p in He and tune the Monte Carlo simulation - A second test is planned before summer. - The obiective is to be ready to mount in DAFNE in mid 2009, for a relative short data taking( (1 month, including intallation and debugging), to assess the ability to discover KAIUM at DAFNE

31. CONCLUSIONS In the ~mid of next year, upgraded DAFNE should be at the best of its performance in the present configuration, with the actual experiment ending their data taking, on the verge to be heavily “scuffled” to accomodate big spectrometers with big solenoidal magnetic fields for a lenghtly period of tuning and data taking. There is a nice window of opportunity for a “clever” idea that would allow to perform, in a relatively short time on the present configuration of DAFNE, using a set up based on reliable and well known technologies, an interesting experiment able to provide not only new information but, if succesful, having the potential for future, deep developments. Is this the search for KAIUM?